Entropy amplification from energy feedback in simulated galaxy groups and clusters

We use hydrodynamical simulations of galaxy clusters and groups to study the effect of pre–heating on the entropy structure of the intra–cluster medium (ICM). Our simulations account for non–gravitational heating of the gas either by imposing a minimum entropy floor at redshift zh = 3 in adiabatic simulations, or by considering feedback by galactic winds powered by supernova (SN) energy in runs that include radiative cooling and star formation. In the adiabatic simulations we find that the entropy is increased out to the external regions of the simulated halos as a consequence of the transition from clumpy to smooth accretion induced by extra heating. This result is in line with the predictions of the semi–analytical model by Voit et al. However, the introduction of radiative cooling substantially reduces this entropy amplification effect. While we find that galactic winds of increasing strength are effective in regulating star formation, they have a negligible effect on the entropy profile of cluster–sized halos. Only in models where the action of the winds is complemented with diffuse heating corresponding to a pre–collapse entropy do we find a sizable entropy amplification out to the virial radius of the groups. Observational evidence for entropy amplification in the outskirts of galaxy clusters and groups therefore favours a scenario for feedback that distributes heating energy in a more diffuse way than predicted by the model for galactic winds from SN explosions explored here.